Reinforcing cage

ABSTRACT

Reinforcing cage for the wall of a concrete pipe characterized by a pair of helical spaced coils, indexed 180* apart, and longitudinal members woven over and under adjacent coils and mechanically locked thereto, said members being disposed angularly to the planes of the ends of the cage, forming isosceles triangles for resisting torsion in both directions about the cage axis, together with method of making the cage. Various additional optional features may be employed.

United States Patent 1 1 James [4 1 Oct. 15,1974

I 1 REINFORCING CAGE [75] Inventor: Kenneth E. James, Denver, C010.

[73] Assignee: Stressed Pipe Research, Inc.,

Englewood, Calif.

22] Filed: Mar. 12, 1973 211 Appl. No.: 340,019

[52] US. Cl. 138/175, 138/176 [51] Int. Cl F161 9/08 [58] Field ofSearch 138/175, 176, I72; 245/2;

[56] References Cited UNITED STATES PATENTS 1,830,202 11/1931 Jenkins138/175 FOREIGN PATENTS OR APPLICATIONS 798,309 7/1958 Great Britain138/172 Primary ExaminerJames J. Gill Assistant Examiner-Anthony V.Ciarlantc Attorney, Agent, or FirmSheridan, Ross & Fields 57 ABSTRACTReinforcing cage for the wall of a concrete pipe characterized by a pairof helical spaced coils, indexed 180 apart, and longitudinal memberswoven over and under adjacent coils and mechanically locked thereto,said members being disposed angularly to the planes of the ends of thecage, forming isosceles triangles for resisting torsion in bothdirections about the cage axis, together with method of making the cage.Various additional optional features may be employed.

11 Claims, 11 Drawing Figures REINFORCING CAGE BACKGROUND OF THEINVENTION Concrete pipe employed in water distribution systems and thelike, due to its relatively poor strength in tension, is conventionallysteel reinforced with rods or wire extending circumferentially which issubjected to hoop tension and other rods or wire extendinglongitudinally which are subjected to tension in a direction parallelwith the pipe axis. Expansive concrete is now widely used which, uponcuring, causes a pipe section to enlarge slightly in diameter andincrease in length which stresses all of the steel bonded within itswall in tension. This in turn, pre-stresses the concrete in compressionwhich increases the strength of the pipe to resist internal pressure.Thus, when pressurized, the concrete may still be in compression, underwhich it has its maximum strength, or may be stressed in tension only toan extent well within its tensile strength limitations. US. Pat. No.3,520,968 to Kreston is exemplary of the construction referred to whichdiscloses circumferential and longitudinal reinforcing members whichprestress the concrete in compression. One of the difficulties with suchconstruction and others similar thereto is that the reinforcing members,which form a cage, provide little torsional strength to the cage duringthe handling thereof or to the pipe section during its use. Also, toprovide a stable cage during handling and casting of the concrete it isessential that the crossing members be secured together at many pointswhich is time consuming and costly to manufacture. Further, if smoothwire or rod is employed for the longitudinal reinforcing, it isdifficult to obtain the requisite bond between same and the concrete,which problem was recognized in the patent referred to.

SUMMARY OF THE INVENTION The present invention provides an improvedreinforcing cage for concrete pipe which obviates disadvantages of theprior art which, in its broader aspects, is characterized by two helicalcoils indexed 180, similar to the threads of a double thread screw, andlongitudinal reinforcing members which extend angularly to the planes ofthe ends of the cage in right and left hand directions. These provideinherently rigid triangles to resist torque in both of oppositedirections. They are interwoven over and under the two coils referred toso they are locked therebetween without need of welds or ties at pointsof crossing. Additionally, they are distorted into longitudinalserpentines which serve to improve the locks and longitudinal bond andbetter absorb shear stresses between same and the concrete, asdistinguished from straight smooth members which tend to slip relativeto the concrete during the expansive curing. The triangles are isoscelesshaped with respect to their bases at the ends of the cage and, ifsuitably overlapped, may cross forming an X shaped pattern. Optionaladditional features include non-angular longitudinal members inside oroutside of the cage or both, interwoven members, or bars having bondstrength since each longitudinal member is mechanically locked along itslength to the two coils.

In accordance with the foregoing, the principal objects of the inventionare to provide improved concrete pipe reinforcing cages which areinherently strong to resist hoop tension, longitudinal tension andtorque in both of opposite directions about its axis.

Another object is to provide improved concrete pipe employing suchcages.

Another object is to provide improved bond between longitudinallyextending reinforcing and the concrete.

Another object is to provide a cage, the various parts of which may belocked together with simple bends or mechanical fasteners, obviating orminimizing welds, wire ties, or the like.

Still further objects, advantages, and salient features will become moreapparent from the detailed description to follow, the appended claims,and the accompanying drawing to now be briefly described.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of areinforcing cage, a concrete pipe in which it is embedded being shown bydotted lines;

FIG. 2 is an end elevation as viewed in the direction of arrow 2, FIG.1;

FIG. 3 is a plan of the cage of FIG. 1 as developed to planar form;

FIG. 3A is a like partial development of an alternative form of theinvention;

FIG. 4 is a section taken on line 4-4, FIG. 3;

FIG. 5 is a longitudinal section, similar to FIG. 4, illustratingadditional reinforcing disposed inside the cage coils and extendingparallel to the axis thereof;

FIG. 5A is a like section, illustrating the additional reinforcingdisposed outside of the cage coils;

FIG. 5B is a like section, illustrating the additional reinforcing wovenbetween the cage coils;

FIG. 5C is a like section, illustrating the additional reinforcing asbars having appreciable cross'wire holding ability to maintain precisespacing of the circumferential coils because preformed serratedprojections may be mechanically locked to each of the cage coils:

FIG. 6 is a section taken on line 6-6 of FIG. 3; and

FIG. 7 is a section taken on line 7-7, FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to thedrawing, and first to FIGS. 1 to 4, the subject of the inventioncomprises a cylindrical cage formed of a first strand 12, wound as acoil having spaced convolutions, a second like coil 14, the convolutionsof which are disposed between the convolutions of the first coil, andangularly disposed strands 16 which are woven over and under adjacentcoils 12, 14, as best shown in FIG. 4. The construction, as just brieflydescribed, may be better understood by a description of a preferredmethod of making same, to now be described.

A suitable collapsible rotatable mandrel (not shown) may be providedonto which strand material may be fed to form spaced convolutionssimilar to the method of making coil springs with spaced convolutions.The free end of strand 12 is first temporarily affixed to the mandreland then wound onto the mandrel one full turn.

The free end is then affixed to the running portion of I the strand toform a planar end ring 18. At the point of affixation the strand 12commences as a helical coil of desired axial length. The running portionis then severed from the supply of strand material and affixed in likemanner to form another planar end ring 18 at the other end. Strands 16are then helically wound around members 18 on top of the coil justdescribed and their ends temporarily secured to the mandrel. Asillustrated in FIGS. 1 and 2, strands 16 are in pairs, forming isoscelestriangles, the end rings forming the bases thereof. Also, adjacent legsof adjacent triangles cross each other midway between the end rings toform X" configurations. The end of strand 14 is next affixed to an endring at a point 180 to the .point of affixation of strand 12 aspreviously described. It then starts a helical coil and continues to theopposite end ring to which it is affixed in the same manner as describedfor strand 12. The second strand 14 thus lies on top of all of angularlyextending reinforcing members 16 and the convolutions are also disposedaxially midway between the convolutions of the first strand 12, thisarrangement being analogous to the configuration of a double thread inwhich the lead is twice the pitch (distance between adjacent threads).An important feature in winding the second strand 14 is that it bemaintained under sufficient tension to bend members 16 into a sinuous orserpentine form as best shown in FIG. 4. The hills and valleys thusformed, lock the first and second strands in predetermined axiallyspaced relationship equal to the pitch therebetween. The opposite freeends of each member may then be secured to the end rings by hook shapedbends 17 and the assembly removed from the mandrel after collapsingsame. A hook shaped bend 17, as just referred to, is illustrated in FIG.7 and one manner of securing the first coil together to form end ring 18is illustrated in FIG. 6, wherein a U-shaped clip 19 is compressedaround the strand.

Referring now to FIG. 3A, strands 12, 14 are wound in the same manner aspreviously described. Two variants are illustrated which may be employedsingly or in combination. Firstly, strands 16 do not cross as shown inFIG. 3, and secondly, additional reinforcing strands 20 are providedwhich extend parallel to the axis of the cage. As will be apparent,these may be employed with the FIG. 3 construction when desired. Strands20 may be affixed to the cage in various manners to now be described.

Referring to FIG. 5, strands 20 may be disposed inside the cage after ithas been removed from the mandrel and their ends bent around the endrings as previously described. In the FIG. A construction strands 20 aredisposed outside the cage and their ends secured to the end rings inlike manner. FIG. 5B differs essentially from FIGS. 5 and 5A in thatstrands 20 are woven over and under adjacent convolutions l2, 14. Aswill be apparent, in this construction these strands are disposed on topof the first coil after it has been formed on the mandrel in the samemanner as member 16, the difference being that they are disposedparallel vwith the cage axis rather than helically therearound.

FIG. 5C illustrates another form of longitudinal reinforcing members 20Aformed as a flat bar which is so punched to provide tabs or serrations22 which may be bent around coils 12, 14. As illustrated, such bar isdisposed inside the cage but may be disposed outside thereof if sodesired. The number of angularly spaced bars employed around the cage,as with the number of strands 20, may be selected as desired, dependingupon design considerations, some of which will now be de scribed.

As previously referred to, the pre-stressing of expansible concrete pipeis well known as exemplified by the Kreston patent wherein reinforcingcircumferential steel is provided to increase the stress limit of theconcrete in radial directions (hoop tension) and also longitudinal steelfor reinforcing in the longitudinal or axial direction. Such steel,however, has little or no substantial effect on torsional strength ofthe pipe which is essentially shear in a plane perpendicular to the pipeaxis. The difficulty of obtaining adequate bond between the longitudinalsteel and concrete has been recognized, such as disclosed in the Krestonpatent. It will now become apparent that an important and genericconcept of the present invention provides greatly improved torsionalresistance of the cage (and consequently the pipe) in both of oppositedirections by reason of the angular relationship of reinforcing members16. Additionally, the present arrangement of woven longitudinal wiresprovides improved bond to the concrete for transferring longitudinalstress by reason of the undulations therein as contrasted to straightand smooth rods which tend to slip relative to the concrete.Additionally, the undulations mechanically lock the several componentsof the cage in predetermined relationship to prevent movement from theiroptimum positions during handling, such as transport, and during thecasting operation.

The selection of the particular cage features, or combination thereof,as disclosed in the several modifications, will usually be a matter ofengineering selection taking into consideration the factors of expectedstresses and economy of manufacture. In general, the circumferentialsteel will first be selected to provide the requisite hoop tensionresistance which involves selection of steel diameter and pitch of thecoils. An angular configuration of members 16 would normally be nextselected, both as to steel diameter and number of such elements requiredto resist both applied torsion and the longitudinal prestressing forces.These members are, of course, placed in state of tension as the concreteexpands and thus resist the torsional shear; they also are subjected tocomponents of stress in the axial direction. In some instances they maybe so selected that they resist the combined stresses in which caseaxial longitudinal members 20 may be omitted. In some instances, andparticularly where torsional requirements are relatively low, it may befound more economical to add members 20 rather than to design angularmembers 16 to withstand both torsional and longitudinal stresses.

What is claimed is:

l. A reinforcing cage for use within the wall of concrete pipe,comprising:

a. a first strand of reinforcing material, such as steel wire or rod,forming a first coil with axially spaced convolutions,

b. a longitudinally extending pair of strands disposed on the top of thefirst coil at angular positions therearound and in a configuration suchthat said pair forms right and left hand helices,

c. a second like strand forming a second coil, the convolutions of whichare disposed between the convolutions of the first coil, the tensiontherein being sufficient to distort the longitudinally extending strandsat the points of crossing with both coils into generally sinusoidal formhaving valleys therealong, the valleys forming locks to maintain the twocoils in axially spaced relationship, and

d. means securing the ends of the two coils together,

forming an end ring at each end of the cage.

2. A cage in accordance with claim 1 wherein the pair of longitudinalstrands is disposed in such manner that a strand of one crosses a strandof another at a point between the ends of the cage.

3. A cage in accordance with claim 1 wherein the pair of longitudinalstrands is disposed in such manner that each forms a substantiallyisosceles triangle, with an end ring forming the base thereof.

4. A cage in accordance with claim 1 including other longitudinallyextending strands disposed substantially parallel to the axis of thecage.

5. A cage in accordance with claim 4 wherein said other longitudinallyextending strands are woven between the two coils.

6. A cage in accordance with claim 4 wherein said other longitudinallyextending strands are disposed inside of the cage.

7. A cage in accordance with claim 4 wherein said other longitudinallyextending strands are disposed outside of the cage.

8. A cage in accordance with claim 4 wherein said other longitudinallyextending strands comprise at least one serrated member mechanicallylocked to each of the coils.

9. A cage in accordance with claim 1 wherein the wall of the concretepipe is formed of concrete adapted to expand upon curing and setting,whereby: said coils are subjected to tensile stress, producingcircumferential compressive stress in the concrete; and, saidlongitudinally extending strands resist torsional stresses in both ofopposite directions about the axis of the pipe and also resistlongitudinal stress.

10. A cage in accordance with claim 1 including means securing thelongitudinally extending strands to the end rings.

11. The construction set forth in claim 1 in combination with theconcrete pipe.

1. A reinforcing cage for use within the wall of concrete pipe,comprising: a. a first strand of reinforcing material, such as steelwire or rod, forming a first coil with axially spaced convolutions, b. alongitudinally extending pair of strands disposed on the top of thefirst coil at angular positions therearound and in a configuration suchthat said pair forms right and left hand helices, c. a second likestrand forming a second coil, the convolutions of which are disposedbetween the convolutions of the first coil, the tension therein beingsufficient to distort the longitudinally extending strands at the pointsof crossing with both coils into generally sinusoidal form havingvalleys therealong, the valleys forming locks to maintain the two coilsin axially spaced relationship, and d. means securing the ends of thetwo coils together, forming an end ring at each end of the cage.
 2. Acage in accordance with claim 1 wherein the pair of longitudinal strandsis disposed in such manner that a strand of one crosses a strand ofanother at a point between the ends of the cage.
 3. A cage in accordancewith claim 1 wherein the pair of longitudinal strands is disposed insuch manner that each forms a substantially isosceles triangle, with anend ring forming the base thereof.
 4. A cage in accordance with claim 1including other longitudinally extending strands disposed substantiallyparallel to the axis of the cage.
 5. A cage in accordance with claim 4wherein said other longitudinally extending strands are woven betweenthe two coils.
 6. A cage in accordance with claim 4 wherein said otherlongitudinally extending strands are disposed inside of the cage.
 7. Acage in accordance with claim 4 wherein said other longitudinallyextending strands are disposed outside of the cage.
 8. A cage inaccordance with claim 4 wherein said other longitudinally extendingstrands comprise at least one serrated member mechanically locked toeach of the coils.
 9. A cage in accordance with claim 1 wherein the wallof the concrete pipe is formed of concrete adapted to expand upon curingand setting, whereby: said coils are subjected to tensile stress,producing circumferential compressive stress in the concrete; and, saidlongitudinally extending strands resist torsional stresses in both ofopposite directions about the axis of the pipe and also resistlongitudinal stress.
 10. A cage in accordance with claim 1 includingmeans securing the longitudinaLly extending strands to the end rings.11. The construction set forth in claim 1 in combination with theconcrete pipe.